Variable reluctance core



Jan. 25, 1949. R. A. PFUNTNER ETAL 2,460,145

VARIABLE RELUCTANCE CORE Filed Jan. 23, 1948 Inventors: -Richard A. Pfuntn er,

Franklin R. DEntrem ont,

Their Attorneg.

Patented Jan. 25, 1949 VARIABLE RELUCTANCE CORE Richard A. Pfuntner, Sangus, and Franklin R. DEntremont, Lynnfleld, Mass, assignors to General Electric Company, a corporation of New York Application January 23, 1948, Serial No. 4,026

1 Claim.

This invention relates to magnetic induction apparatus and more particularly to variable reluctance induction apparatus It is often desirable in induction apparatus to be able to control the reluctance of the magnetic circuit. Many other quantities may thus be affected by the variation of reluctance. In the case of a transformer the exciting current and therefore the total current may be restricted within limits; the phase relationship between current and voltage may be altered thereby controlling the power factor; the circuit impedance may also be changed. Thus, by regulating the reluctance of a magnetic induction device other dependent quantities may be controlled.

In accordance with this invention the reluctance of magnetic induction apparatus is varied by enclosin laminated core sections in nonmagnetic wrappers and controlling the area of contacts of these core sections.

It is an object of this invention to provide a new and novel induction apparatus core construction whereby the magnetic reluctance of the core may be varied.

It is another object of this invention to provide a simple means of changing the reluctance of a magnetic core by varying the area of the gap separating the two core halves.

It is a further object of this invention to provide a variable reluctance magnetic core whose adjustment is rapid, simple and positive, and which possesses excellent stability characteristics and whose reluctance can be easily controlled within limits previously difiicult to obtain.

In the drawing Fig. 1 is a perspective view of a particular embodiment of the invention illustrating, by way of example, its application to the construction of a transformer core. Fig. 2 is a cross-sectional view taken through the section 22 of Fig. 1. Fig. 3 is an exploded view of the main components of the transformer core. Fig. 4 is a perspective view of the L-shaped laminations from which the core is constructed.

Referring now to the drawing there is shown therein by way of example a transformer core I which is formed from two substantially identical halves 2 and 3, each half being made up of separate stacks of L-shaped laminations 4 which have a main body 5 and a short leg 6 which is perpendicu ar to the body 5. Groups of L-shaped laminations 4 are bound as a unit by a wrapper I made of a suitable nonmagnetic material, such as brass, and adjacent stacks 4 are oriented so that the short leg 6 is alternately at opposite ends of the transformer core I'. As shown inthe drawing only half of the laminated stacks 4 are wrapped in the nonmagnetic material 7. The stacked L-shaped laminations 4 of each half 2 and 3 of the transformer core I are bound as a unit by two hollow rivets 8 which pass through the stacked L-shaped laminations l and the nonmagnetic wrapper I, and are fastened to the clamping devices 9, I0, and II. Clamps I0 and II are identical except clamp Iii has two added wings I2 and I3 which have drilled in them mounting holes I4 and I5. The clamps 9, I0, and II are crimped at I6 so that the'clamping arm of each core half will pass over the other half of the core I. The clamps 9, I0, and II have elongated slots I! for the fastening bolts I8 and I9 which pass through them and through the hollow rivets 8, which hold the core sections 2 and 3 together. Thus the two halves 2 and 3 of the core I, when mounted as a unit, may be placed in such relationship to one another that the area of contact between the L-shaped laminations 4 of each core half 2 and 3 may be varied. The air gap between the two halves 2 and 3 of the transformer core I is maintained by the nonmagnetic wrappers l and the reluctance of the transformer core I is varied by changing the area of contact between the two halves 2 and 3 of the core I.

Since the core sections 2 and 3 are bound together by rivets 8 through which are passed the adjusting screws it and is there is no'change in the reluctance of each half 2 and 3 of the core I due to tightening of the screws I8 and I9 since the screws I8 and i9 apply pressure only to the rivet 8 and not to the stacked laminations 4. This core construction has the advantage of using only one shape of punching to form the laminations 4 and thus presents a feature of added economy in manufacture. Also, since each half 2 and 3 of the core is substantially identical the manufacturin process is simplified. By way of example, a particular application of this core construction is for the purpose of adjusting the phase angle diiference between the primary and secondary currents in an instrument current transformer. The angle desired is only in the order of 2 so that a very small air gap is needed. However, since this angle must be constant, stability of the gap is essential. If a conventional gap in the core were used its length would be in the order of .0005" which wou d be very diificult to adjust or maintain. By increasing the area, as in this construction, the same reluctance can be obtained by increasing the length of the gap directly proportional to the area. The construction shown provides several times the 3 area and, hence, several times the length of the conventional gap. Since the length is fixed by the nonmagnetic wrappers and the area is ad justed, excellent control is obtained and, very good stability results.

While there has been shown and described a particular embodiment of this invention it will be obvious'to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claim to cover all such changes and modifications as fall within the .true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

An adjustable reluctance core for induction apparatus comprising, in combination, two laminated parts having interfltting multiple tongue and groove joints, nonmagnetic wrappers around al- .ternate groups of laminations in each part for providing nonmagnetic gaps between the sides of the interiitting tongues and grooves in said joints, hollow clamping members extending through each 4' core part for firmly holding its wrapped laminations together, and adjustable means for controlling the degree of closure 01 said joints, said adjustable means including additional clamping members extending through said hollow clamping members.

RICHARD A. PFUNTNER. FRANKLIN R. D'ENTREMONT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,080,177 Lucas May 11, 1937 2,133,919 Fries Oct. 18, 1938 2,141,554 Reichard Dec. 27, 1938 2,180,759 Kneisley Nov. 21, 1939 FOREIGN PATENTS Number Country Date 709,923 France Aug. 14, 1931 

